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a different way to get rid of boost lag?

7K views 71 replies 22 participants last post by  Calvinball 
#1 ·
discussing all things turbo with a friend of mine last night. boost problems came up with his 04 eclipse N/A with a turbo kit. while we were trouble shooting his dad came by and says," bolt a blower on it. no more lag, just like my (600hp) impala. there, fixed." and walked away leaving us to ponder. well, our engines Are build for boost. lots of it. has it been done? even as a experiment? a blown 2.0...it would at least look/sound cool. roots and vane supers are LOUD n whiny. and no lag, theyre always boosting. hmmmmm
 
#62 ·
Oh heck ya. Sorry I really did know that....I'm just on my first coffee of the usual four by now. Leeeetle slow this morning.

Do the variable vane turbos alter the pitch of they're blades like a helicopter or do they change the compression chamber? I've never really looked into it but we just had a ford eco boost Taurus in for tires.
 
#63 ·
There are many different ways to incorporate variable geometry turbines. Most of them use a 'flapper' or wiper arm to alter the AR or the angle of attack on the turbine I believe. I don't know of any that actually change the blades at all. Again, a waste gate (such as the one in a Subaru and most other gasoline powered turbo cars) is an example of a variable geometry turbine.
 
#64 ·
IIRC, the most common form of VGT implementation is using a nozzle to direct the exhaust across the inducer through the exducer... this effectively changes the A/R of the turbine allowing quicker spool. Effectively like a 7cm^2 housing at low load and a 9cm^2 housing at high load.
 
#65 ·
Getting a quicker boost level in a smaller chamber then changing to more volume at pressure in the higher load/rpm range? Makes since to me, kinda. I'm sure there is a million different things I'm missing though lol. But with adaptability like that would it make it harder or easier to tune on a engine like ours? Just bolting up a bigger turbo doesn't seem to me like it would perform( at the same levels) as well as a smaller variable turbo. Although no denying the punch of the bigger( maybe higher volume? I'm no expert for sure) turbo
 
#66 ·
The downside to variable geometry turbos is the complexity and cost involved upfront, as well as the fact that you now need a control system of some form.

Take the waste gate as an example.

Without it, you simply bolt up a well specified turbo to an engine and let it go. This is more in the industrial and diesel world.

Now in a gasoline engine, you have a larger operating range over which you want the turbo to be efficient. Hence, they spec the turbo to a smaller output, and make the turbine overly large to limit it back out if it's efficency volume.
 
#67 ·
Let's not forget how the supercharger works also. Ya you won't have turbo lag but u don't make all your power till your about to shift. When our turbo spools up, u get ALL your boost right then and keep it throughout the rom range till u shift, or if you have an auto! Till u let off the gas
 
#68 ·
Not quite true. A twin-screw supercharger or a twin-lobe supercharger (roots blower) makes boost linearly with rpm (when the compressor is correctly matched to engine size). That is, max boost arrives at max rpm where the car has the potential to make the largest power. This mimics the powerband of a NA car. A centrifugal supercharger offers increased simplicity and improved adiabatic efficiency, but boost is built exponentially to RPM. Consequently,a turbocharger makes boost only over a very specific airflow band. No WRX built OEM holds boost to redline, like a properly designed blower. However, few superchargers charge the incoming air to the pressure a turbocharger does...

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